Improving Estimates of Gross Primary Productivity by Assimilating Solar‐Induced Fluorescence Satellite Retrievals in a Terrestrial Biosphere Model Using a Process‐Based SIF Model

Abstract

Over the last few years, solar-induced chlorophyll fluorescence (SIF) observations from space have emerged as a promising resource for evaluating the spatio-temporal distribution of gross primary productivity (GPP) simulated by global terrestrial biosphere models. SIF can be used to improve GPP simulations by optimizing critical model parameters through statistical Bayesian data assimilation techniques. A prerequisite is the availability of a functional link between GPP and SIF in terrestrial biosphere models. Here we present the development of a mechanistic SIF observation operator in the ORCHIDEE (Organizing Carbon and Hydrology In Dynamic Ecosystems) terrestrial biosphere model. It simulates the regulation of photosystem II fluorescence quantum yield at the leaf level thanks to a novel parameterization of non-photochemical quenching as a function of temperature, photosynthetically active radiation, and normalized quantum yield of photochemistry. It emulates the radiative transfer of chlorophyll fluorescence to the top of the canopy using a parametric simplification of the SCOPE (Soil Canopy Observation Photosynthesis Energy) model. We assimilate two years of monthly OCO-2 (Orbiting Carbon Observatory-2) SIF product at 0.5°(2015-2016) to optimize ORCHIDEE photosynthesis and phenological parameters over an ensemble of grid points for all plant functional types. The impact on the simulated GPP is considerable with a large decrease of the global scale budget by 28 GtC/year over the period 1990-2009. The optimized GPP budget (134/136 GtC/year over ) remarkably agrees with independent GPP estimates, FLUXSAT (137 GtC/year over 2001) in particular and FLUXCOM (121 GtC/year over 1990. Our results also suggest a biome dependency of the SIF-GPP relationship that needs to be improved for some plant functional types.

Photosynthesis in a Changing Global Climate: Scaling Up and Scaling Down in Crops

“…These multispectral and hyperspectral methods are especially amenable to high-throughput analyses and can be incorporated into different HTP platforms such as aerial drones (Sankaran et al, 2015;Kanning et al, 2018), tractors (Scotford and Miller, 2004;Andrade-Sanchez et al, 2014), and carts (Thompson et al, 2018). Previously, SIF had been shown to be correlated with canopy photosynthesis (Yang et al, 2015) and used to estimate gross primary productivity (Bacour et al, 2019). Passive measurements of photosynthetic traits like SIF can be carried out extremely rapidly and at multiple times during the growing season.…”

Carbonyl Sulfide: Comparing a Mechanistic Representation of the Vegetation Uptake in a Land Surface Model and the Leaf Relative Uptake Approach

“…GPP proxies are also used, such as Solar-Induced Fluorescence (Norton et al, 2019;Bacour et al, 2019), isotopic composition of atmospheric CO2 ( 18 : Farquhar et al, 1993;Welp et al, 2011;13 : Peters et al, 2018) and 65…”

Wide Discrepancies in the Magnitude and Direction of Modelled SIF in Response to Light Conditions

“…Assimilation of OCO-2 SIF in ORCHIDEE brings the magnitude of both GPP and SIF in closer agreement with observations. This improvement is driven by decreases in leaf photosynthetic capacity (Vcmax, LAImax, leaf age, SLA, Bacour et al, 2019), which decreases the magnitude (but not shape) of APAR closer to observed values (Fig 2), and leads to improvements in GPPyield and SIFyield (Fig 3). Nevertheless, after the assimilation there are still disagreements in SIFyield vs GPPyield relative to the measured quantities ( Fig 6).…”

“…Adapted to drought stressed Mediterranean species including high temperature correction (Tol et al, 2014;Flexas et al, 2002) BETHY-exp3 Adapted to drought stressed Mediterranean species (Flexas et al, 2002) ORCHIDEE (Bacour et al, 2019) ORCHIDEE-exp1 prognostic Adapted to needleleaf species (Porcar-Castell et al, 2011) and unstressed Mediterranean species (Flexas, 2002), with added dependence on PAR, temperature, and φP Parametric representation of SCOPE (v1.61) to emulate radiative transfer within canopy for PSI/II.…”

“…2018) andBacour et al (2019), respectively. For the two models, an ensemble of parameters related to photosynthesis (including optimal Vcmax) and phenology were optimized for several plant functional types.…”